Radio receiving system



Aug 23, 1938. T. A. MARSHALL RADIO RECEIVING SYSTEM Filed July l, 1936@E /wam Patented '23, 1938 `fill?INIT,ITD STATES Q; 2,127,525;` Y Revio@GEW-ING SYSTEM* f w n. Thomas A. Marshallr'vSaPiedro, Calif?` l u"Appli'ca'tionfJulyi, ,ieserseghNgffsssaf iciaivms. (crest-8) A yl(ri-mitm'. 'under the mi, 'of "March 3, i883, 'as

and atmospheric disturbances in thereception of signals.

One of the objects of my inventionis topro- 1 'vide' a 'radio Areceivingsystem which will' clearly and efliciently receive signals of lvaryhigh` carrierffrequencies which arev especially subject Vto distortionand'critical under )control so that reliable reception thereof isdiicult.

" Another/'object of myinvention isto,v provide a raidioreceivingcircuitA for'thefreception of high 'frequency signal energy in which theuse of highly selective circuitsuis made possible byfthe'ad- Jjustmentof the carrier frequencyover consid- "e'rable, ranges of variation topass the selective circuits to the exclusion of dstortingandlinterfering energy.

Al further object ofmy inventionl isgto make possible thev employment oftone discrimination inthereception of continuous Wave signals atvultra-lngh frequencies. l

" Still another object of my inventionv is to provide a superheterodyneradio-receiving system fory the reception of ultra-high frequencysignals, 'wherein tonel discrimination is made possible by modulatingthe intermediate frequency current at a stable audio frequency andkeying the audio modulation by the signal received.

A still further object of my invention is to provide vasuperheterodyneradio receiving system 'for-the reception of ultra-high frequencysignals, wherein the signals are impressed on the first detector-and areeffective in the intermediate frequency amplifier -under the controlr ofVan, loscillating-current operative to iniiuence the output ofthconversion oscillator; the' intermediate Vfrequency' amplifier beingrparticularly selective to pass only the desired frequency band. l

' Another object of my invention is to provide' a ys'uperlfieterodyneradio receiving system for the reception of ultra-high frequency signalsWherein the signals are intermittently passed vto the intermediatefrequency amplifier, and 4all distortion, atmospherics, andman-madestatic are effectively excluded from the output during the periodsbetween the intermittently passed signals. f' Other and further objectsof my invention reside in -the circuit arrangement and modifications'thereofl hereinafter more fully described, with reference to theaccompanying drawing, whichis a..schematic diagram :of the circuitemployed v-in the receiving system of my invention.

` .;In the reception of signals at ultra-high'fre-l Llective circuit inthe receiving system in vorder -to'exclude distortion arising fromfrequency l Y ,amendedAprilB 1928;,370 O. G4757) lfil/[yfnventionrelates broadly tcsuperheterovtlyfneradio receivers and moreparticularly to a modulationand rharmonics of the modulating signals,andjalsof.V interfering energy such asarises from atmosphericdisturbances,`manmade static,

orinterinali'circuit'imperfections.y In C.'W. re-

-ception, the lpractice "known, as tone discrimination isextremelyus'efuland has been' made practical in the receptionof'comparatively low frequencies. ,But so far, k,tone discriminationhasnot vbeen satisfactorilyaccomplished in the field of ultra-highfrequencyVreception due to variations in the local oscillator frequency and inthe transmitter'frequency. Any variation in the oscillator frequency forobtaining `heterodyne reception of the incoming frequency'will changethe beat frequency, which is usually made 1,000`cycles 'and amplifiedvin a peakedaudio'- amplifier. Should the beat frequency bechanged evenslightly, tone discrimination Willnorlongerbe useful, and'if thefrequency of lthetransmitter varies,'the sig- -nall will likely not beheard; For vlovv frequency reception, better stability of frequency andless percent variations'in ther operation of the transmittlers and localoscillator are obtained and tone discrimination is practical.

,In the reception of voice modulated high frequency Waves, the vpracticeof tone discrimination is Anotapplicable but/an analogous operation,employing the same circuit arrangement, is possible ywith merelyanadjustment of the frequencies of operationas will `hereinafter be morefully set forth. n

ATone discrimination in C. W. reception at high and'ultra-highfrequencies is obtained in the system of my invention v'by using atunedaudio system, and a super-heterodyne receiver,l and byk modulating thelintermediate frequency current by varying theoscillator output With amodified type `of relaxation oscillator which is adjusted to 1,000cycles. Thel intermediate frequency currentl is therefore modulated at'1,000 cycles, and is detected by an ordinary rectier'instead of by the-beat frequency oscillator method. Thus, all signals are receivedas ifthey were actually transmittedwith a-modulation of 1,000 cycles, andtone discrimination isvpossible.y

Referring -to the drawing in more detail, I provide an antenna l and apre-selector tuning circuit 2 connected With the input of a radiofrequencyamplier-stage '3.th`roughfa coupling condenser 14. A balanced,non-oscillating rst dentector circuit employing electron tubesl 5 and 5'has the inductancel in the'input circuit thereof coupled with theinductance 1 which is connected in ,the voutputcircuit of the radiofrequency amplifler 3. An inductance 8 is connected between Ithe anodesofthe tubes and 5 and hasl a center rtap connection -8 thereto forconnection to vthe anodes of the lbalanced detector. The inductanceJ8.is coupledwith the input circuit of the first detector through theinductance 6, but oscilla- I and I0', inductance I I connected with thecontrol grids ythereof and inductance IZ, coupled with inductance II,connected with the anodes thereof. in shunt with inductance Il, and isoperable to control the frequency of oscillation of the conversionoscillator in the usual manner` through a gang control arrangementwith.tuning con-l densers I5 and I6 in the radio frequency amplier 3 and thefirst detector circuit, respectively, as indicated by the dotted lineII..

, lIhe output of the conversion oscillator is coupled with the firstdetector, wherein it beats with energy at the received frequency toproduce currents at'the desired intermediate frequency, through theinductace 8 via the high frequency coupling condenser I3, which isv ofapproximately 100 mmf. capacity, the conductor vI 9, and the center tap8. The output of the first detector, at the intermediate frequency isVfed through the tap 8' and conductor 20 to the intermediate frequencyamplifier as will be hereinafter more fully considered.

In addition to and in cooperation with the usual functions in asuperheterodyne receiver, I provide a relatively low frequencyoscillatorY 2|, which is a modified relaxation type of electron tubeoscillator and will generate an output of constant frequency. Meanscomprising a variable resistor 22, connected in the cathode circuit ofthe oscillator 2i, is provided for adjusting the frequency of operationof the oscillator 2l. In C. W. reception, as now being considered, thisfrequency may be an audio frequency of 1000 cycles per second.Measurements on thisoscillator, operatingat 1000 cycles, showed that itsfre.-

quency varied but 3 cycles over a period of five hours. A variable anodevoltage of volts plus or minus 10 percent gave a frequency variation ofapproximately 10 cycles. Novariation infrequency was observed by varyingthe heater voltage from 2 to 2.5 volts.

The low frequency auxiliary oscillator l2I is connected with theconversion oscillator through a high frequency choke coil 23, a lowfrequency coupling condenser 24, which is of approximately 1 mfd.'capacity, conductor 25, `and center tap I2' on the inductance I2,whereby the output of the low frequency oscillator 2l modulates theoutput of the conversion oscillator. In the case of C. W. reception, theoutput of the conversion oscillator is modulated by a constant 1000cycle per second audio frequency. In'the first detector, this modulatedcurrent entering at 8lr divides between the two halves of the inductance8 on either side of the center tap andqequally affects the control gridsof the tubes 5 and 5 by reason Yof the coupling between inductances 8.and 6. When no signal is received on antenna I and in inductance l, themodulation of 1000 cycles will not be heard by thev listener because ofthe absence of an intermediate frequency current. When a signal isreceived and passes through inductance 1, the control grids of the tubes5, 5', are oppositely affected thereby because of the unbalancedcoupling of the inductance l, and a beat frequency will be generatedfrom the combination of the signal and the local oscillator output. Thefirst detector thus produces an output at the beat frequency which isthe intermediate frequency A variable condenser Iis connectedV auxiliaryoscillator 2! current of the superheterodyne receiving system, and thisintermediate frequency current is modulated at 1000 cycles from theoutput of the auxiliary oscillator 2|.

The modulated intermediate frequency current is fed through conductor 20to the interrnediate frequency amplier stages 26 and 27 and to thesecond detector 28 in the output of which appears the 1000cycle'modulation in the characterof the signal received. In the outputof the second detector, I have provided a low pass filter 29 and a bandpass filter 30 in order to effectively exclude all energy except the1000 cycle signal. This is possible because of the stability of the 1000cycle wave which is generated in the Peaked audio frequency amplifierstages 3| .and 32 complete the receiving circuit to the telephonereceivers 34. The listenerhearing the constant 1000Ycycle note inthe(characterV of the signal may therefore easily Y discriminate in tonebetween the signal and any interference that may be present in thetelephones.

I have shown in the drawing merely the terminals of the power supplycircuits and the connections at x, which interconnect the heaterelements in the various tubes shown. 'Volume control means are shown at35 and 36; and choke coils 3l and bias resistors 38 are shown distrib-,uted in the power connections as required. Bypass condensers 39likewise are provided `where necessary.

In the system of kmy invention as shown and described, static appears tobe received as a highly damped oscillation and does not unbalance thedetector by'aoting in the inductance 'I as a signal. It is, therefore,not heard in the telephones at 1000 cycles when Va tuned vaudio systemisemployed as shown. It appears also that crashes and noise do noteffectively unbalance the rst detector, so that clear reception is hadon .all high `frequency bands. Thus, the system of my invention isextremely useful in the elimination of noise, static and internalamplifier noise, and reception at the 'high frequencies is, therefore,greatly improved.

A further useful advantage of the system of my invention will be seenin` ultra-high frequency multiple reception work, that is, intermittentreceptionfrom a number ofcommunication stations all transmitting at or.near the same frequency. Heretofore such operation has not beensuccessful on ultra-high frequencies due to the fact that crystals usedfor controlling the frequencies of the Several transmitters are not all`ground to the same frequency but to frequencies differing by severalkilocycles. Higher accuracy in the grinding of the crystals to insuresubstantially identical frequencies of operation is irnpracticable. Byemploying a modulated intermediate frequency current in thesuperheterodyne receiver, the circuits can be made to cover as wide arange as 16 kilocycles by adjusting the intermediate frequency band passtuning sys- "tem, or by obtaining from the second ldetector through thebeating of incoming signals of various frequencies with the output ofthe conversion oscillator and the output of the auxiliaryoscil1ator,'beat frequencies which will be passed by peaked intermediatefrequency amplifier circuits.

-The latter instance will obtain, for example, wheny anoscillatorfrequency of 20,465 kilocycles isrnodulated by a 1000cycleoscillation to produce beats ofV 20,466 and 20,464 kilocycles.Considering that these beat frequencies Will also beat to produce a 2kilocycle note and that the second. harmonic of the modulation is 2kilocycles, further beat frequencies of 20,461 to 20,464 and 20,466 to20,469 kilocycles, as well as the fundamental frequency o-f 20,465kilocycles, will be present in the first detector to beat with thesignal energy. Signal energy therefore of any frequency between thelimits of 19,996 and 20,004 kilocycles will produce a beat frequency inthe output of the first detector of 465 kilocycles which will be passedby a peaked 465 kilocycle intermediate frequency amplifier.

Considering, now, voice modulated currents received at the antenna Ifrom a single transmitter operating'at ultra-high frequency, and thefrequency of which is susceptible of rather broad variation, such aswithin the range above noted in which a number of C. W. transmitterswere considered operating. Such a voice modulated current, varying infrequency, can be received by the system of my invention in a mannersimilar to that just previously described. One important adjustment isrequired to be made, namely, in the frequency of the auxiliaryoscillator which must obviously be of super audible frequency in orderthat the output thereof will not be heard in the telephones. Thisadjustment can be made by merely 'varying the resistance 22 in thecathode circuit of the auxiliary os'cillator 2l. Coupling condenser 24may also be varied to transmit the higher frequency more efficiently;and the lters 29 and 30 also may be adjusted for the modified operationof the system. Also, as only one station is to be received, theintermediate frequency amplifiers 26, 21, may be limited to respond onlyto a narrow frequency band which embraces the voice modulations. Theadvantages of noise suppression, and distortion removal and prevention,noted with respect to the operation of the system of my invention in C.W. reception,

`obtain also in the reception of voice modulated currents.

While the system of my invention is primarily intended for use in C. W.reception on ultra-high frequencies, as hereinbefore set forth, I desireit understood that modifications may be made within the scope of myinvention along the lines indicated with respect to the reception ofvoice modulated currents, and along other lines, and that novlimitations upon my invention are intended except as are imposed bytheappended claims.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is as follows: y

1. In a superheterodyne high-frequency continuous wave signal receivingsystem, in combination, a first detector comprising a balanced electrontube circuit having a balanced input circuit and a balanced outputcircuit in coupled relation, a local oscillator, means for modulatingsaid local oscillator at a constant audible frequency, means forimpressing the output of said modulated oscillator on said firstdetector through said output circuit in balanced relation, means forimpressing incoming continuous wave signals on said first detector inunbalanced relation whereby said electron tube circuit is unbalanced andcurrent flows inthe said output circuit at-.

the beat frequency of said incoming signal and the local oscillation, inthe character of the incoming signal, and modulated at said constantaudible frequency, an intermediate frequency amplifier operative at saidbeat frequency, a second detector, and a peaked audio frequencyamplifier for selectively amplifying said modulation.

2. In a superheterodyne high-frequency voice modulated signal receivingsystem, in combination, a first detector comprising a balanced electrontube circuit having a balanced input circuit and a balanced outputcircuit in coupled relation, a local oscillator, means for modulatingsaid local oscillator at a constant inaudible frequency, means forimpressing the output of said modulated oscillator on said firstdetector through said output circuit in balanced relation, means forimpressing incoming voice modulated signals on said first detector inunbalanced relation whereby said electron tube circuit is unbalanced andcurrents of beat frequencies are produced in said first detector, anintermediate frequency amplifier, certain of said beat frequenciesproduced in said first detector corresponding to the frequency ofoperation of said intermediate frequency amplifier, a second detector,and an audio frequency amplifier for amplifying the voice modulationsdetected in said second detector.

3. In a superheterodyne high-frequency signal receiving system, afirstdetector comprising a balanced electron tube circuithaving a balancedinput circuit and a balanced output circuit, center-tapped inductancesin said input and said output circuits arranged in coupled relation, anda third inductance coupled with said centertapped inductances, meansincluding the centertapped inductance in said output circuit forimpressing modulated local oscillations on said input circuit inbalanced relation, means including said third inductance for impressingsignal energy on said input circuit in unbalanced relation, and anintermediate frequency amplifier operatively connected with said firstdetector through the center tap of said inductance in the output circuitthereof for receiving modulated oscillations of beat frequency in thecharacter of the signal energy.

4. AIn a superheterodyne high-frequency signal receiving system, a firstdetector comprising a pair of electron tube devices having inputcircuits connected in push-pull relation and output circuits connectedin parallel relation, centertapped inductances in said input and saidoutput circuits arranged in coupled relation, and a third inductancecoupled with said center-tapped inductances, means including thecenter-tapped inductance in said output circuits for impressingmodulated local oscillations on said input circuit in balanced relation,means including said third inductance for impressing signal energy onsaid input circuit in unbalanced relation, and an intermediate frequencyamplifier operatively connected with said parallel connected outputcircuits for receiving from each of said electron tube devices modulatedoscillations of beat frequency in the character of the signal energy.

THOMAS A. MARSHALL.

